chore: upgrade Loki 2.9.0 to 3.6.1 with tsdb/v13 schema (refs #98)

- Update Loki image from 2.9.0 to 3.6.1 in docker-compose.yml
- Migrate schema from v11 to v13, store from boltdb-shipper to tsdb
- Update storage_config to use tsdb_shipper with new index paths
- Remove deprecated shared_store config (removed in Loki 3.0)
- Disable structured metadata (not needed for current setup)
- Preserve 30-day retention policy (720h)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

config/loki/config.yml

@@ -15,24 +15,23 @@ ingester:
 schema_config:
   configs:
     - from: 2020-01-01
-      store: boltdb-shipper
+      store: tsdb
       object_store: filesystem
-      schema: v11
+      schema: v13
       index:
         prefix: index_
         period: 24h
 
 storage_config:
-  boltdb_shipper:
-    active_index_directory: /loki/boltdb-shipper-active
-    cache_location: /loki/boltdb-shipper-cache
-    shared_store: filesystem
+  tsdb_shipper:
+    active_index_directory: /loki/tsdb-index
+    cache_location: /loki/tsdb-cache
   filesystem:
     directory: /loki/chunks
 
 compactor:
   working_directory: /loki/compactor
-  shared_store: filesystem
 
 limits_config:
   retention_period: 720h  # 30 days
+  allow_structured_metadata: false